Moving it to BR1 could only work if it lost its HEAT completely. Some people say AP and HE mix would still be OP for BR1, but not having any MG and a very small ammo capacity will limit the vehicle no matter what.
Keeping it in BR2 while exchanging its AP rounds with either more HEATs, or giving it half HEAT, half HE would be a start to make it decent.
Giving it the better BR3 HEAT Type C round with 115mm of penetration is dangerous - because you dont want to end up turning that famous infantry support vehicle into a better tank hunter than STUG F.
A third option would be to give it both types of HEAT rounds and some HE - to limit its ammo capacity against heavy armor.
But no matter what - 7 smoke shells are so terrible for that tank, they take away a big amount of ammo capacity. STUG A should get 2 smokes max - if any at all.